This invention relates to biologically active compounds, and it is concerned with providing by means of chemical derivatisation, a technique whereby the behaviour of many biologically active compounds, such as drugs and agricultural chemicals, may be favourably modified.
There is a great interest in the medical community to investigate and improve the transport efficiency of drugs to the site of action in the patient. The work has mainly been focused on resorption of a drug from the intestine to the blood stream, although transport across other biological barriers often plays an important role in obtaining the necessary therapeutic effect in the treatment of many diseases like cancer, infections, inflammations, CNS disorders etc. The transport across the cell membrane is often a main impediment to achieve optimal effect with a therapeutic compound.
Over the last decades drug resistance in the treatment of malignant and infectious diseases has become increasingly prevalent and is now regarded as a serious clinical problem. The development of drug resistance can be due to a number of mechanisms, but quite often relates to a triggering of the normal mechanisms whereby microorganisms and cells clear toxic compounds to subtoxic levels. One example is the development of multi-drug resistance (MDR) in cancer cells. In this case MDR frequently relates to a cellular membrane protein pump by which the cells-achieve a very efficient efflux of toxic compounds. In a clinical situation, the treatment of a tumour with a cytostatic drug, cells with the most potent protein pump can preferentially survive, and these cells may proliferate to a new tumour which may be resistant to treatment with a variety of different drugs. Similar mechanisms of action may be responsible for the lack of effect seen in other therapeutic areas, for instance with anti-malarial drugs.
Several techniques to try to circumvent resistance mechanisms in the clinic are known. For example, the co-administration of a Ca2+ channel blocker such as verapamil or an immunomodulating agent like cyclosporin, have been tried out. However, no significant improvements have been reported so far.
There have been several proposals in the literature for improving the therapeutic index, bioavailability, membrane passage, organ targeting, etc of therapeutic compounds by combining the compounds with fatty acids so as to form either chemically coupled derivatives or physical mixtures.
Thus, for example, EP-A-393920 discloses that anti-viral nucleosides and nucleoside analogues which are derivatised with long chain (C16 upwards) acyl groups have advantages as compared with the parent compound. It is stated that the fatty acid portion of these molecules preferably are made up of polyunsaturated fatty acids, such as xcex3-linolenic or linoleic acid.
US-A-3920630 teaches that 2,2xe2x80x2-anhydro-aracytidine and its 5xe2x80x2-O-acylates have the same general biological and therapeutic activity as anti-viral agents as ara-cytidine itself. The compound 2,2xe2x80x2-anhydro-5xe2x80x2-O-oleyl-ara-cytidine is specially mentioned.
EP-A-56265 discloses esters of arabino-furanosyl-thymine (Ara T) with saturated acids having 1-17 C-atoms.
From PCT/WO90/00555 there are known lipid derivatives linked, especially through aphosphate group, to the 5xe2x80x2-position of the pentose group of a nucleoside. The purpose of this derivatisation is to make the nucleosides more lipophilic so that they could be included into liposomes, which are preferentially taken up by macrophages and monecytes, cells which are found to harbour the HIV virus. It is stated that a targeting effect is thereby achieved.
The anti-viral and anti-cancer activities of nucleoside analogues are directly linked to intra-cellular phosphorylation of the administered drug. This biochemical transformation is normally effectuated by viral and/or cellular enzymes. To improve the effect WO96/25421 discloses phospholipid derivatives of nucleosides with relatively short chain (C14 or less) saturated or unsaturated fatty acids.
The art has also sought to improve the characteristics of other classes of pharmaceutical substance through derivatisation with fatty acids.
For example, WO96/22303 teaches that the pharmokinetic profile and mode of delivery of several different categories of therapeutic compounds (corticosterones, opioids and opioid antagonists, anti-viral nucleosides, cyclospprins and related cyclopeptides, folate antagonists, catecholamine precursors and catecholamines and alkylating agents containing a carboxylic acid group) can be altered by conjugating them to one to three acyl derivatives of fatty acids through the use of a linker/spacer group which includes a tromethamine or ethanolamine derivative. Palmitic acid is the preferred fatty acid.
Lipophilic pro drugs of several NSAIDs are known from H. Bundgaard et al (International Journal of Pharmaceutics, 43 101-110 1988) and V. R. Shanbhag et al (Journal of Pharmaceutical Sciences, 149 Vol 81, No 2, February 1992). In addition to the pro drug aspect, reduced GI irritation is reported. EP-A-0195570 suggests that the administration of gamma-linolenic and dihomo-gamma-linolenic acid in conjunction with NSAIDs reduces the side effects shown by the NSAIDs when taken on a continuing basis.
U.S. Pat. No. 5,284,876 teaches the use of docosahexaenoic acid amides of dopamine as per oral prodrugs in the treatment of CNS disorders.
Physical mixtures containing fatty acids/fatty acid derivatives used as so-called penetration enhancers both with dermal and per oral administration are known from PCT/US94/02880 and PCT/SE96/00122.
As indicated, many of these prior proposals concern fatty acid derivatives of anti-viral nucleosides and nucleoside analogues. It is indeed not surprising that this should be so as it has long been known that certain polyunsaturated fatty acids attack viruses. In EP-A-0642525 we ourselves taught that the anti-viral effect of nucleosides and nucleoside analogues can be highly potentiated through reaction with oleic acid (cis-9-octadecenoic acid), elaidic acid (trans-9-octadecenoic acid), cis-11-eicosenoic acid or trans-11-eicosenoic acid, to form the corresponding 5xe2x80x2xe2x80x94O-monoester. We have shown that the beneficial effects which can be obtained from these four specific monounsaturated, xcfx89-9 C18 or C20 fatty acids are superior to those generally obtainable through fatty acid derivatisation.
We have now surprisingly found in accordance with the present invention that the properties of numerous different biologically active compounds may be favourably modified by derivatisation with an xcfx89-9 C18 or C20 monounsaturated fatty acid. The present invention thus provides a widely utilisable but simple technique for enhancing the value of many drugs and agricultural chemicals, for instance.
Broadly, the present invention in one aspect provides a lipophilic derivative of a biologically active compound containing in its molecular structure one or more functional groups selected from alcohol, ether, phenyl, amino, amido, thiol, carboxylic acid and carboxylic acid ester groups, other than a nucleoside or nucleoside analogue, said lipophilic derivative being characterised by a molecular structure in whichthe or at least one said functional group of said biologically active compound is replaced by a lipophilic group selected from those of the formula: RCOOxe2x80x94, RCONHxe2x80x94, RCOSxe2x80x94, RCH2Oxe2x80x94, RCH2NHxe2x80x94, xe2x80x94COOCH2R, xe2x80x94CONHCH2R and xe2x80x94SCH2R, wherein R is a lipophilic moiety selected from cis-8-heptadecenyl, trans-8-heptadecenyl, cis-10-nonadecenyl and trans-10-nonadecenyl.
In one preferred embodiment of the present invention, the biological effect of a therapeutic compound is improved by derivatising the compound with a n-9 C18 or C20 monounsaturated fatty acid. We present below a detailed discussion of the application of this invention to drugs selected from the following groups:
1. cancer drugs;
2. antiinflammatory drugs
NSAIDs
adrenocorticosteroids;
3. antibiotics and other antibacterial agents;
4. antiparasitic drugs;
5. CNS drugs;
6. cardiovascular drugs; and
7. anticoagulants
However, the invention is broadly applicable to any compound which is pharmacologically active and which possesses in its molecule one or more functional groups capable of conjugating with an n-9 C18 or C20 monounsaturated fatty acid. Thus, for example, the present invention may also be used to improve the biological effects of medicinal compounds of the following types, for instance analgesics, fungicides, antihyperlipidemics, antiemetics and diagnostics.
The lipophilic derivatives of therapeutically-active compounds in accordance with the present invention may be formulated with pharmaceutically acceptable carriers and excipients by conventional procedures well known to those skilled in the art. The dosage rates will be correlated with those of the mother drug, although in cases where the lipophilic derivatives of the invention strongly potentiate the effect of the mother drug it may be possible to reduce the dosage from normal levels.
Although the beneficial effects of the present invention have been demonstrated on well-established drugs, it is believed that similar improvements are likely to be exhibited by other drugs which are still in the course of development. That is to say, the postulated explanation for the improved properties which we have observed with lipophilic derivatives of this invention, is of general application and not restricted to any specific mechanism for therapeutic activity.
A particularly valuable property which we have found exhibited by some of the lipophilic derivatives of therapeutically active compounds in accordance with the present invention is that they overcome drug resistance. Although we do not wish to be bound by theory, it is believed that the lipophilic derivatives of this invention interact in some manner with membrane protein pumps so that the cells are inhibited from clearing the active (toxic) compounds, thus enabling the concentration of the active compounds to be sustained at a therapeutically beneficial level for longer periods. In any event, the present invention leads also to the possibility of combatting the effects of drug resistance by the co-administration of a mother drug and a lipophilic derivative of that drug in accordance with the present invention. Suitably, the mother drug and lipophilic derivative thereof will normally be presented in the same pharmaceutical preparation for ease of administration, although in some cases it may be preferred to present the mother drug and lipophilic derivative in separate unit dosage forms. The dosage of the lipophilic derivative, relative to that of the mother drug can be determined by appropriate tests but generally will range from 1:1 to 1000:1 by weight.
As previously indicated, the invention is generally applicable to any compound having biological activity and not just drugs.
Another economically important class of biologically active compounds are products used in agriculture and horticulture, for example pesticides, fungicides and herbicides. Agrochemicals vary widely, both in structure and in their modes of action. For instance, there are several well-recognized routes of uptake; for example plants may take up the active compound either through the root system or directly through the leaves or stem of the plant, while a pesticide may be taken up either through a plant which the pest attacks or by direct contact. Lipophilic derivatives of agrochemicals in accordance with this invention are found to have enhanced take up-potential both byplants and by insects and other pests. Moreover, the present derivatives help to combat pesticide resistance which, like drug resistance, is a growing problem.
Other classes of biologically active compounds which can with advantage be derivatised in accordance with the present invention include food and feed additives such as conserving agents, fragrances and spices.
The lipophilic derivatives of the present invention may be prepared by reacting the parent drug or other biologically active compound molecule with a cis- or trans-n-9 monounsaturated fatty acid, fatty acid alcohol or fatty amine having a chain length of 18 or 20 carbon atoms, or with a reactive derivative of such a fatty acid, fatty alcohol or fatty amine, for example acid chlorides, reactive esters, halogenides or the like. The notation n-9 indicates that the unsaturation is between the 9 and 10 positions counted from the C-terminal of the lipidic moiety. Thus, that fatty acids (and alcohols and amines derived therefrom) which may be used are cis-9-octadecenoic acid (oleic acid), trans-9-octadecenoic acid, (elaidic acid), cis-11-eicosenoic acid and trans-11-eicosenoic acid.
The coupling reaction between the parent biologically active compound and the fatty acid, fatty alcohol or fatty amine compound can be accomplished by a variety of methods known to those skilled in the art. When two or more derivatisable functional groups are present in the parent molecule, then protecting groups or modified synthetic methods may be used to achieve the necessary selectivity in the coupling steps. In general, the progress of the reactions can be followed using thin layer chromatography (TLC) and appropriate solvent systems. When the reaction is completed as determined by TLC, the product is generally extracted with an organic solvent and purified by chromatography and/or recrystallization from an appropriate solvent system. If more than one hydroxyl, amino, thiol or carboxylic group is present in the parent starting material, a mixture of alkylated or acylated compounds may be produced. The individual mono- or poly-derivatised compounds may then be separated by, for instance, chromatography.
Often, the coupling reaction may be accomplished in one-step, and generally the lipophilic derivatives can be recovered as crystals with good stability profiles, which is helpful for successful galenical processing of the finished pharmaceutical product.
The preparative processes which may be used according to the present invention are illustrated by the reaction schemes given below as well as by the working examples given later in this specification.